Removed m_loss from CStructuredOutputMachine

The m_loss has been removed from CStructuredOutputMachine, since this depends on particular solver. A attribute m_surrogate_loss has been added to CPrimalMosekSOSVM, which plays the same role as m_loss before. 

@ppletscher, @iglesias, @vigsterkr What do you think this change? Other points may also need to refine. I haven't done that because there are already lots of files involved.
- These functions put in CStructuredOutputMachine better:
float64_t CStructuredModel::risk(float64_t* subgrad, float64_t* W, TMultipleCPinfo* info=0);
void CStructuredModel::init_opt(...);

- CFeatures* CLinearStructuredOutputMachine:: m_features; seems never
being used, and it's not necessary, since we got m_features in CStructuredModel.

If you think these are okay, I'll update later in this PR.